The invention is based on a spring brake cylinder for brake installations of vehicles, having a spring brake piston which is arranged in the housing of the spring brake cylinder and which can be actuated by means of at least one preloaded spring. The spring brake piston separates a spring chamber which contains the preloaded spring from a spring brake chamber of the spring brake cylinder, which chamber can be ventilated for release and which can be vented for deployment, wherein a circulation device at least for venting the spring chamber directly to the atmosphere is provided.
From the prior art, for example, from DE-A-1 505 574, there are known spring brake cylinders with ventilation devices in which, at the outer wall of the spring brake cylinder within an additional housing, a diaphragm valve mechanism is provided in order to produce a connection between the spring brake cylinder chamber and the spring chamber when the spring brake piston is displaced when the spring brake cylinder is deployed by the preloaded spring. The volume of the spring chamber, which increases in this instance, allows the production therein of a reduced pressure which is decreased by the diaphragm valve mechanism, that is to say, during the displacement of the spring brake piston, the mechanism ventilates the spring chamber with compressed air originating from the spring brake chamber. When the spring brake cylinder is released, the diaphragm valve mechanism blocks the mentioned connection, the compressed air in the spring chamber which is then compressed being discharged by means of an additional ventilation valve in a through-hole in the base of the spring brake cylinder to the atmosphere. Consequently, a relatively high level of complexity is involved in order to carry out a ventilation and venting of the spring chamber of the spring brake cylinder.
In this regard, an object of the present invention is to further develop a spring brake cylinder of the above-mentioned type in such a manner that a ventilation and venting of the spring chamber are carried out with less complexity.
This and other objects are achieved according to the invention by a spring brake cylinder for brake installations of vehicles, having a spring brake piston which is arranged in the housing of the spring brake cylinder and which can be actuated by at least one preloaded spring, and which separates a spring chamber which contains the preloaded spring from a spring brake chamber of the spring brake cylinder. The spring brake chamber can be ventilated for release and can be vented for deployment. A circulation device at least for venting the spring chamber directly to the atmosphere is provided. The circulation device is constructed as a diaphragm valve having at least one resiliently movable outlet diaphragm and at least one resiliently movable inlet diaphragm. The inlet diaphragm and the outlet diaphragm in their basic position are in a closure position, which is characterized in contact with an associated valve seat. In the event of a pressure difference which exceeds a respective minimum pressure value between the spring chamber and the atmosphere, the inlet and outlet diaphragms are controlled into an open position lifted-off of the valve seat in order to increase pressure and decrease pressure in the spring chamber.
The invention makes provision for the circulation device to be constructed as a diaphragm valve having at least one resiliently movable outlet diaphragm and at least one resiliently movable inlet diaphragm, wherein the inlet diaphragm and the outlet diaphragm in their basic position are in a closure position which is characterized in contact with an associated valve seat and, in the event of a pressure difference which exceeds a respective minimum pressure value between the spring chamber and the atmosphere, are controlled into an open position raised from the valve seat in order to increase pressure and decrease pressure in the spring chamber.
The minimum pressure value will be or is reached when the volume of the spring chamber decreases when the spring brake cylinder is released and increases when the spring brake cylinder is deployed. Then, the outlet diaphragm is moved from the closure position into the open position thereof when the volume of the spring chamber decreases when the spring brake cylinder is released and the inlet diaphragm is moved from the closure position thereof into the open position when the volume of the spring chamber increases when the spring brake cylinder is deployed.
It is then possible to dispense with an additional housing as in the generic prior art. Furthermore, the ventilation of the spring chamber when the spring brake cylinder is deployed is no longer carried out by use of compressed air from the spring brake chamber, but instead from the atmosphere, whereby the circulation device is constructed in a very simple and cost-effective manner.
In one aspect of the invention in particular, the at least one inlet diaphragm and the at least one outlet diaphragm are constructed so as to be spatially separated from each other, wherein a separate valve seat is associated with the inlet diaphragm and the outlet diaphragm, respectively. The inlet or outlet characteristic can then be individually adapted to the prevailing pressure relationships.
Furthermore, for example, the at least one inlet diaphragm and the at least one outlet diaphragm are connected to a base member which is retained in a central through-opening in the base of the spring chamber. Then, the base member can be assembled together with the at least one inlet diaphragm and the at least one outlet diaphragm as a pre-assembled unit on the spring brake cylinder.
The base member is preferably constructed in an integral manner from a resilient material, having a retention portion which can be assembled in a positive-locking manner with resilient deformation in an associated through-opening in the base of the spring brake cylinder, wherein there is retained on the base member a retention member, for example, in the form of a retention pin, on which there is formed the at least one inlet diaphragm and/or the at least one outlet diaphragm which cooperates as a diaphragm valve with at least one connection opening formed in the base member or in the base between the spring chamber and the atmosphere.
According to a further development, the base member comprises a resilient material to be retained in a positive-locking manner in the central through-opening in the base of the spring chamber by way of a retention portion which has an undercut cross-section. The retention portion is resiliently deformed from the outer side when the base member is introduced into the through-opening in order, in the assembled end state, to protrude inside the spring chamber in a manner engaging over an inner edge of the through-opening. A very simple method of assembling the base member on the spring brake cylinder is thereby provided.
To this end, the retention portion of the base member may be constructed in a conical manner and may taper in the direction toward the inner side of the spring chamber.
Furthermore, the at least one inlet diaphragm may be arranged on a base face of the base member, which face is directed inside the spring chamber, and the at least one outlet diaphragm may be arranged on an outwardly facing outer face of the base member, wherein the at least one inlet diaphragm and the at least one outlet diaphragm cooperate with a plurality of connection openings between the spring chamber and the atmosphere in a sealing manner.
In this instance, according to a first embodiment, at least one connection opening may be formed in the base of the spring brake cylinder and at least one connection opening in the base member. In this instance, the at least one connection opening in the base may cooperate, for example, with the at least one outlet diaphragm and the at least one connection opening in the base member may cooperate with the at least one inlet diaphragm.
According to a second embodiment, the connection openings may also all be formed in the base member, wherein the at least one inlet diaphragm cooperates with a connection opening or with a group of connection openings and the at least one outlet diaphragm cooperates with another connection opening or another group of connection openings. This second embodiment has the advantage that such connection openings are more simply prefabricated in a base member, which is separated from the spring brake cylinder, than in the spring brake cylinder itself.
In a particularly preferred manner, the at least one inlet diaphragm is connected to a retention pin which is retained in the base member and protrudes radially at right angles from the retention pin.
According to the first embodiment, the inlet diaphragm can be constructed as a disc diaphragm which is integral with a retention pin produced from a resilient material and which, from an end of the retention pin directed inside the spring chamber in a manner protruding radially outward, forms a free disc diaphragm edge which cooperates in a sealing manner with a plurality of connection openings in the base member which are radially spaced from the retention pin.
In this instance, the retention pin is, for example, retained in the base member in a positive-locking manner so as to protrude through a central through-hole of the base member with a head piece, which is expanded in cross-section and which faces outward. The head piece and/or the base member is/are resiliently deformed when the retention pin is inserted into the through-hole of the base member in order in the assembled end state to engage over an outer edge of the through-hole of the base member in a positive-locking manner. The retention pin can thereby be assembled in a simple manner with the inlet diaphragm by means of insertion into the central through-hole of the base member.
In many spring brake cylinders, there is formed on the base of the housing of the spring brake cylinder an annular recess which serves to center the preloaded spring in the spring chamber. Furthermore, with a corresponding construction size of the spring chamber, it may be necessary to ventilate and vent the spring chamber with a relatively large volume of air when the spring brake cylinder is released and deployed. The cross-section provided by the connection openings in the base member may then not be sufficient to transport the air volume which is intended to be supplied or discharged.
In the first embodiment, the at least one outlet diaphragm is therefore formed at the end side on a web of the base member, which web bridges an annular recess in an outer face of the base of the spring brake cylinder, and cooperates with at least one outer valve seat at the edge of at least one connection opening in the base of the spring brake cylinder, wherein the web and the at least one outlet diaphragm are constructed integrally with the base member. The at least one connection opening in the base, in contrast to the connection openings in the base member which then serve exclusively to ventilate the spring chamber, then provides a venting cross-section.
In this instance, the web between the outlet diaphragm and the recess in the base of the spring brake cylinder may be retained on the base by way of a pin which protrudes away from the web and which is retained in a hole in the base in a positive-locking manner. The base member is thereby retained in a secure manner on the spring brake cylinder together with the web and the outlet diaphragm which is formed on the web. Furthermore, the base member together with the web and the outlet diaphragm on the spring brake cylinder may be assembled in a simple manner by way of parallel insertion of the retention portion (see above) and the pin into the associated openings in the base of the spring brake cylinder.
According to the second embodiment, the at least one inlet diaphragm and the at least one outlet diaphragm, when viewed in cross-section, may protrude in opposite directions away from the retention pin in a radially outward direction and may cooperate with diametrically opposing connection openings in the base member.
Furthermore, there may be provision in this second embodiment for there to be formed integrally on the retention pin at the end side contractions and head pieces which are increased in terms of diameter with respect thereto, wherein the head pieces are inserted through openings of the inlet diaphragm and the outlet diaphragm with resilient deformation, in order to form a positive-locking connection with an undercut cross-section between the retention pin, on the one hand, and the inlet diaphragm and outlet diaphragm, on the other hand. The inlet diaphragm and outlet diaphragm are secured to the retention pin in this manner and, at the same time, form an axial securing member for the retention pin in the through-hole of the base member. These measures also contribute greatly to a very simple and cost-effective production and assembly of the spring brake cylinder.
The spring brake cylinder according to the invention may be constructed as a separate spring brake cylinder or may be provided as an integral component of a combined service brake and spring brake cylinder for pneumatic or electro-pneumatic brake installations of vehicles.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.